1. Interactivity of a Multimedia Scene
In various applications such as the internet for example, a multimedia scene is composed of graphical objects and displayed on a screen by the use of a graphical interface. The screen may undergo dynamic modifications interactively, after it is fully downloaded by the rendering terminal. Several types of interaction may modify a multimedia scene:                the execution of scripts or programs triggering the animation of an object in the scene, following an event generated by the user, such as a mouse click on an object containing an interactive link to a page of the internet for example;        automatic updating coming from the server on which the characteristics of the scene to be transmitted are stored.        
In general, any animation or change of form in the scene, generated by a user, corresponds to an interaction on the objects: translation, appearance, disappearance, highlighting, change of properties, etc.
The diversity and complexity of these interactions and of the modifications that they give rise to depend on the service and the application in which the multimedia scene is executed.
2. Coding of a Multimedia Scene
An interactive multimedia scene is described and coded according to a format managing graphical and interactive functionalities thus allowing visual returns and a graphical rendering that are very attractive to the user.
In addition, while many standard graphical formats are static, in the sense that they describe scenes that are not modified over time, new formats, such as the standardized LASER format, allow almost unlimited interactions on graphical scenes.
For this purpose a multimedia scene is broken down into graphical objects, each containing attributes taking numerical values, sometimes predefined. It is possible in particular to count among these attributes elements concerning the animation of the objects making up the interactive scene.
3. Rendering of a Multimedia Scene
An interactive multimedia graphical scene can be executed in the context of various services and applications, offered both by sophisticated devices such as a computer having powerful components (graphics card, high-speed network connection, etc), and devices more restricted in resources, such as wireless telecommunication systems.
Conventionally, for rendering an interactive scene, the multimedia reader of the terminal then uses, according to known techniques, a program module called a rendering engine.
Its role is to produce the rendering of a synthetic image, from the scene description, by calculating all the surfaces of the various objects making up the graphical object scene.
The rendering engine then explores all the characteristics and attributes of the objects making up the scene, in particular the attributes defining its animations. It functions in at least one rendering mode that is in a position to manage a very complex scene. It is also responsible for executing the modifications of the scene when the user interacts with at least one of its interactive components.
In general, a multimedia reader may have available several operating modes, including at least one complete mode and at least one “simplified” mode, faster, but not capable of managing the full complexity of the standard.
When there is no protocol for dynamic modification of the scene, the rendering engine is capable, during the exploration of the scene, to choose the most appropriate rendering mode, the most simple, which can however satisfy all the rendering options. The choice of the most appropriate rendering mode must be made at the start of the rendering and cannot be called into question later. It is a difficult choice that determines the rendering of the scene throughout its duration.
When a protocol for dynamic modification of the scene is available, the rendering engine is no longer capable of making these analyses and these rendering mode choices: this is because, at any time, a dynamic modification may call into question the choice of simple rendering mode by adding a parameter that requires a more complex rendering mode. However, as the choice of the rendering mode must be made once and for all at the start, the rendering engine can, as the only solution, merely apply the most general and the most complex rendering mode.
Systematically, in the presence of a dynamic scene modification protocol, the content of the “animation” element must be loaded into a different scene from the initial scene. The rendering engine must therefore be capable of rendering two independent scenes, which results conventionally in an increase in complexity in terms of implementation.
4. Drawbacks of the Prior Art
Conventionally, in the rendering technique known from the prior art, the rendering engine has no means enabling it to determine in advance the level of complexity of a scene, that is to say knowing whether the latter will be caused to undergo interactive modifications on at least some objects in the multimedia scene. Such modifications require changing to a more complex rendering mode, even if the analysis of the initial scene allowed it to be assumed that a lighter and simpler rendering mode would offer better use of the resources of the terminal.
However, the inventors have found that a major part of the services or applications implement and execute interactive scenes with a low level of complexity, in terms of interaction and/or multimedia rendering, which do not require the use of the most general rendering mode, the most expensive in terms of resources.
Since the rendering engine does not know in advance the content of the scene received, it is therefore not in a position to make substantial simplifications affording a saving in resources, both in terms of calculation time or downloading, which would however be advantageous in the case of devices or terminals, for example radio communication ones, having available small calculation resources, or at the very least limited ones.
In other words, a multimedia reader, even if it has several operating modes available, is incapable of ensuring that a simplified operating mode may prove to be adequate in terms of multimedia rendering, before having received all the scene to be rendered.
In the absence of information, the reader can then only make a choice of security by choosing a complex operating mode, in order to provide all the dynamic modifications of the scene that may occur subsequently.
Another drawback of current techniques is related to the fact that they cause a relatively slow functioning of the rendering engine.
Moreover, an additional drawback of multimedia scene rendering techniques stems from the fact that there exists no specification concerning the optimization of the rendering of interactive multimedia scenes on terminals, for example radio communication terminals.
Finally, up to the present time, this problem did not exist in the descriptions of scenes relying on the SVG, SMIL, HTML, etc standards, which include no possibility of dynamic modifications of scenes that may arise after the loading of the initial scene.
This is because, in SVG/SMIL in particular, the “initial” scene represents the entire scene. The SVG/SMIL multimedia reader must examine the whole of the scene before beginning to retrieve it through the graphical interface of a terminal and therefore before making all the optimizations and simplifications that it judges adequate for this.
Moreover, in SVG, the text-rendering, image-rendering, shape-rendering and color-rendering attributes indicate to the rendering engine whether it should prefer a smooth rendering mode, which would have the drawback of being slow, or fast. In the latter case, the rendering will be degraded.